All twins born in Minnesota from 1936 through 1955 will be identified through birth records. At least 80 percent of the surviving intact pairs will be recruited to participate in the Minnesota Twin-Family Registry. We expect to recruit 4,200 pairs of same-sex and 1,000 pairs of opposite-sex twins, 4,000 spouses of participating twins, and at least 500 twin families consisting of both twins and their spouses, at least one offspring of each twin and, in some cases, pairs of same-sex siblings of the twins and/or both parents of the twins. Twin recruiting is by graded incentive so that we can compare, on demographic, interest, and personality variables, the similarity of easily recruited pairs with that of pairs in which one or both twins are reluctant to participate, i.e., twin pairs not usually studied. All subjects will complete a Biographical Questionnaire including health, education, occupation, and zygosity information, most subjects will also complete a battery of personality and interest inventories. As part of the Minnesota Study of Twins Reared Apart, the same measures are being obtained from 100 pairs of twins separated in infancy and reared apart and from the adoptive siblings of 50 of these twins. The data will be grouped into 4 age-match sub-samples to be analyzed by replication. These data will provide a unique opportunity for assessing by model-fitting techniques the relative importance of additive genetic, nonadditive (including epistatic or "emergenic") genetic variance, shared and unshared environmental contributions to individual differences in basic traits of personality and interest. The data will also permit a unique assessment of assortative mating, spousal assimilation, and parental influences in respect to these same variables. It is intended that the Twin-Family Registry will be maintained as a continuing research resource.